1. Field of the Invention
This invention relates to an improvement in apparatus for detecting irregularities in the surfaces of materials.
2. Description of the Prior Art
Apparatuses for detecting irregularities in the surfaces of materials have been used extensively for detecting irregularities such as cracks, defects and the like in surfaces of materials such as steel or aluminum web, and the like, by means of detecting the light reflected by the surfaces of these materials. Apparatuses of this kind, wherein a laser is usually utilized as the source of light, detect with high speed, cracks, damage and the like in the surfaces of a planar steel member rolled by a rolling machine, for example.
Usually, in apparatuses adapted to be used with wide webs, the width of the surface to be scanned is divided into zones and a separate laser source is used for each zone. The beam of each laser is scanned widthwise in each zone so that the scan lines are in alignment with each other.
Apparatuses using multiple beams can, of course, inspect the surfaces of materials at higher speeds than apparatuses utilizing only a single beam. Hence, in such multi-beam apparatus no increase of the scanning speed or enlargement of the laser beam cross section is necessary for increasing the operating speed.
However, prior apparatuses using multiple laser beams have a drawback in that the detectors responsive to the reflected beams receive not only the individual reflected beam which is sought to be detected, but also reflected beams from adjacent scanning zones due to adjacent and aligned positions of the scanning zones. Hence the detection accuracy of such devices is not always very good.